The present invention pertains to methods for controlling the configuration and motion of a personal vehicle equipped with one or more wheels or other ground-contacting members.
Personal vehicles (those used by handicapped persons, for example), may benefit from actively stabilization in one or more of the fore-aft or left-right planes. Operation of a balancing vehicle is described in U.S. Pat. No. 5,701,965 (incorporated herein by reference, and referred to herein as the xe2x80x9c""965 patentxe2x80x9d). Personal vehicles may advantageously be stabilized whether or not the vehicles are self-propelled, whether or not the vehicles may be guided by the occupant of the vehicle or by an assistant, and whether or not the vehicles may operate in a balancing mode. Vehicles of this sort may be more efficiently and safely operated employing control modes supplementary to those described in the prior art. A personal vehicle may be referred to in this description, interchangeably, as a xe2x80x9ctransporter.xe2x80x9d
In accordance with a preferred embodiment of the invention, terms are provided in both the wheel and cluster control laws of a vehicle so that the amount of effort required by a rider to control the vehicle by virtue of the location of the center of gravity is significantly reduced. Thus, most riders are able to climb or descend stairs unaided by an assistant. The addition of terms referenced to a front and rear angle allows the rider to lean the vehicle between the front and rear angle with relatively low exertions because the pitch gain can be set to a small value while a large gain can be used with the front and rear angles to maintain a fast rotation of the cluster during stair climbing. The front and rear angles are updated throughout the stair climbing process thereby allowing the rider to vary the position of the vehicle CG (center of gravity) with very little effort.
In accordance with embodiments of the invention, a wheel control law is provided that mirrors the cluster control law in that front and rear angles are added to the wheel control law. The wheel control law differs slightly from the cluster control law in order to assure that during stair climbing the wheels can only move in the rearward direction. In addition, a damping term is included in the wheel control law which changes depending on the wheel direction and has the effect of accelerating the wheel into the riser while decelerating the wheels in the forward direction. This change alters the behavior of the vehicle at the top or bottom step and provides for a safer transition at the beginning and end of stair climbing.
In accordance with further embodiments of the invention, there is provided a brake pitch control algorithm. This is a safety feature that monitors the cluster and wheel motor temperature during stair climbing. If the cluster or wheel motor overheats and fails during portions of the stair climb, the vehicle may fall. If the temperature exceeds a preset value, the brake pitch controller turns off the motor amplifiers and controls the motion by modulating the cluster brakes. The controller places the vehicle in a configuration where all four wheels are on the stairs thus placing the vehicle in a statically stable configuration with respect to gravity and preventing the rider from continuing in stair mode. The algorithm continues to monitor the motor temperature and if the motors cool sufficiently, will resume stair mode in order to allow the rider to exit from the stairs.